A conventional device applies a detection wave and collects reflection data from an object to be detected, performs parabolic approximation or elliptic approximation on the sequence of points of the reflection data, and performs a rotation correction process on this approximated data to calculate the position of a corner of an obstacle such as a parked vehicle (for example, refer to patent reference 1). Rotation correction means a method of correcting the reflection position of the detection wave in such a way that the angle which a straight line connecting between the position of a sonar for applying the detection wave and the reflection position forms with the moving path of the sonar decreases with increase in the ratio of the amount of variation of the detected distance between the sonar position and the reflection position to the amount of travel of the sonar.
However, while the approximate expression is changed according to the length of the obstacle in this method, it becomes impossible for the approximated curve to approximate the real corner with a high degree of precision as a straight line portion of the obstacle which consists of a linearly-created sequence of points of the reflection data increases in length. More specifically, there is a tendency for the measurement accuracy of the parking space to get worse.
Furthermore, patent reference 2 discloses a conventional device for making a rotation correction to each reflection position by calculating a rotation-corrected angle for each reflection position acquired in time sequence by using the fact that the ratio of the amount of variation of the detected distance to the amount of travel of a sonar becomes nearly equal to the sine in the direction of the normal to an object face. A rotation-correction reflection point which is positioned outermostly with respect to the direction of travel of the sonar, among all rotation-corrected reflection points, is estimated as the position of a corner of the obstacle.
Furthermore, in the removal of noise from the sequence of points which consist of the reflection positions, the reflection data about n points continuous in time sequence are acquired, and noise determination is carried out according to whether or not each point is positioned within an effective range which is set up according to the traveled distance of the vehicle from a reference point. For example, the Nth reflection position is deleted when the data about the next (N+1)th reflection position does not exist within a circle centered at the Nth reflection position and having a fixed radius.
Also in the case of using the method described in patent reference 2, it becomes impossible for the approximated curve to approximate the real corner with a high degree of precision as a straight line portion of the obstacle increases in length, and there is a tendency for the measurement accuracy of the parking space to get worse.
The present invention is made in order to solve the above-mentioned problem, and it is therefore an object of the present invention to provide a parking support device that can measure a parking space with a high degree of precision on the basis of the position of a corner of an object to be detected.